Known methods for upgrading refinery naphtha streams have inherent drawbacks. Feedstock streams mainly comprising hydrocarbons containing four to five carbon atoms (C4-C5) are typically characterized by high octane ratings, but also high vapor pressures that exceed government specifications for liquid transportation fuels such as gasoline. These specifications often require either upgrading of the C4 and C5 hydrocarbons to products characterized by lower vapor pressure or exclusion from the gasoline pool.
C6+ naphtha feed streams typically exhibit low vapor pressure, but are typically also characterized by a low octane rating and must be upgraded to products comprising a higher-octane rating via naphtha reforming. Conventional naphtha reforming efficiently and selectively converts naphthenes (cycloalkanes) into aromatics, but is non-selective for the conversion of paraffins to aromatics, resulting in low aromatics yields from paraffins feeds. Further, C4-C5 paraffins are not upgraded in conventional naphtha reformers, since these paraffins cannot form aromatics. Thus, while solutions for isolated hydrocarbon streams exist, a practical process for efficiently upgrading a naphtha stream comprising both light C4-C5 hydrocarbons as well as C6+ hydrocarbon components currently does not exist.
Described herein are unique processes and systems that improve the reforming of a hydrocarbon feedstock by selectively reforming discrete sub-components of the feedstock using at least two structurally-distinct reforming catalysts. Advantages of the inventive processes and systems include (but are not limited to) increasing the yield of a liquid hydrocarbon reformate that is characterized by at least one of an increased octane rating and decreased vapor pressure. A further advantage is a decreased rate of reforming catalyst coking and deactivation.